Oily wastewaters containing emulsified hydrocarbons are produced in various industries including the steel and aluminum industries, chemical processing industry, automotive industry, laundry industry and crude oil recovery and refining industries. Typical emulsified hydrocarbons include lubricants, cutting fluids, tars, grease, crude oils, diesel oils, gasoline, kerosene, jet fuel, and the like.
The emulsified hydrocarbon in the water is typically present in the range of tens to thousands of ppm. This residual hydrocarbon must be removed prior to discharge of the water to the environment or reuse of the water in the industrial process. In addition to ecological concerns and governmental regulations, efficient removal of emulsified hydrocarbons is also vital for economic reasons as use of water containing emulsified oil in industrial processes eventually results in decreased production and increased operational costs for the industry involved.
One of the most effective methods of removing the emulsified oil is through the use of water clarifiers. Historically, dry polymers, solution polymers, water-soluble dispersion polymers, inverse emulsion latexes and metal ions have been used to treat the produced water. Each material has its own advantages and disadvantages. Dry polymers have the benefit of reduced shipment cost (less volume due to the lack of the solvent) but for the same reason they require special equipment in order to dissolve them prior to use in the field.
Latex polymer's performance is quite superior and they are used frequently; however, they have their own set of problems. They have a narrow treating range often resulting in over-treatment, and they have to be inverted prior to use. Therefore, like dry polymers they require special equipment in the oil field. This equipment is very often unavailable, and the use of uninverted products may cause a lot of plugging problems in the feeding system.
Solution polymers are often very diluted due to their limited solubility. They are also usually unable to flocculate the dispersed oil, thus requiring another chemical (either latex or dispersion polymer) to accomplish this. Thus, they are used to break reverse emulsions in the field, while the second, “finishing product”, is added in the final stages of water clarification.
Metal ions, such as Fe3+, Zn2+, Al3+, etc. have been used to break reverse emulsion for a long time, but recent government regulations have restricted their levels in discharged streams. Although effective at breaking reverse emulsions, they also require another chemical to flocculate the oil.
Dispersion polymers offer solutions to some of these problems, but they are not totally problem-free either. Though water soluble, their very high molecular weight and associated with this viscosity changes upon dilution require very sophisticated feeding system, which often hinders their application in the field.
Some of the best from above listed water clarifiers have also been used to remove residual oil from the quench water in dilution steam systems of petrochemical industry. In the ethylene manufacturing plant, water is used in the quench column (tower) to cool the gas leaving the primary distillation tower (primary fractionator). In the base of such a tower, hot quench water is separated from condensed hydrocarbons and sent back to a dilution steam generator, while the oil is returned to the system as a reflux. When the oil and water are emulsified, the separation of the two phases is often aided by the use of chemical additives, otherwise the residual oil can foul the dilution steam system and cause a additional fouling problems downstream. The separation of the two phases should occur rapidly due to short system retention times; therefore, it is imperative that the products possess superior performance.
Accordingly, there is an ongoing need for efficient, economical and environmentally friendly methods of clarifying oily wastewater.